This invention relates generally to a means and method for communicating with a programmable biologically implanted medication system and more specifically to a means and method for establishing a coherent inductive communications link with a programmable biologically implanted medication system for transmitting commands to the implanted medication system and for receiving telemetry data from the implanted medication system.
An example of such a programmable implantable medication system is disclosed in U.S. Pat. No. 4,373,527 issued Feb. 15, 1983.
In the field of biologically implanted devices such as cardiac pacers and medication infusion pumps, efficiency and accuracy are the paramount concerns. As can be appreciated, an inaccurately programmed or controlled cardiac pacer could mean death to the patient. Likewise some medications being infused by an implanted infusion pump would be lethal if overdosed and would be ineffective if underdosed. The devices must also be efficient to prevent power failure and to preclude having to replace power supplies in the implanted device after short periods of time. In the field of implantable devices there has been an increased utilization of digital circuitry due to the advances made in digital technology. The advantages of digital circuitry correlate to the requirements of an implanted device, i.e., efficiency and accuracy of control. Initially cardiac pacers were simple analog devices which had performance reliability. With improvements in digital techniques and developing techniques for fabricating compact, low power digital circuitry, digital implanted devices, such as cardiac pacers, have become more popular. In addition, the development of much improved batteries has also encouraged the use of digital control techniques in implanted devices.
In nearly all of the devices that are implanted in the human body it is either absolutely necessary or highly desirable to have the ability to reprogram the operating parameters and to monitor the performance of the device, both historically and contemporaneously. To add flexibility to the use of implanted devices and to free the patient from restrictive close ties to a medical center, it is desirable that the implanted device be reprogrammable by the patient as well as the doctor and that the implanted device be reprogrammable by the doctor from a remote location. Because of the reprogrammability by the patient, the desirability and the necessity of having an historical record of the operation of the implanted device is increased.
The nature of some implanted devices is such that it is desirable to reprogram the operating characteristics very often. For example, with an insulin dispensing implanted device it may be necessary that the patient reprogram the implanted device after each meal or snack with data reflecting the size of the meal and the contents of the meal. This is necessary so that the insulin dispensing device dispenses insulin at a rate and profile closely matching a healthy pancreas. Because of the large number of reprogrammings it is necessary that the reprogramming procedure is accomplished with little or no power drain to the power supply in the implanted device.
As can be appreciated, the success of an implanted device with respect to their life sustaining purpose and their life threatening potential is highly dependent upon the ability to establish a reliable, accurate and verifiable communications link to and from the implanted device. The communications system must have the ability to rapidly establish reliable communications, communicate accurate command data and reprogramming data, verify the receipt of the communicated data by the implanted device and to communicate historical operational data from the implanted device. Because of the precision necessary in the administration of insulin, drugs, chemotherapeutic agents, etc., to the human, the communications link must be highly resistant or impervious to external extraneous noise. To decrease the probability of failure of the implanted device, which would require surgery to replace it, a system with as much complexity as possible residing in the external device must be provided. The implanted device must have the ability to accurately discriminate between command data and programming data. The system must have a method to confirm communications link integrity, verify transmitted data and advise of the operational status of the implanted device.
The prior art discloses various means and methods for communicating with an implanted device. The prior art also identifies a number of problems associated with reliably communicating control data to an implanted device. However, none of the known prior art provides all of the above-stated requirements for a reliable, accurate, verifiable communications link. In a number of the prior art systems, a programming signal must be converted by the implanted device into a proper logic form for control of the implanted device. In these devices it must be assumed, i.e., there is no direct verification, that the signal was accurately received by the implanted device. Another problem in a number of prior art devices is that accessing the implanted device is conducted independently of transmitting the control data. Absent means of verification, the result is that there is no control over ensuring accurate data input after access has been accomplished even though the implanted device may be reliably isolated from being reprogrammed by external, extraneous signals or interference in the communications link. Interference can cause either improper control data input or cause the implanted device to improperly decode the control data.
The U.S. Pat. No. 4,126,139 to Walters et al., entitled "Method and Means for Receiving Parameter Control Data in an Implantable Heart Pacer", discloses a heart pacer employing a digital parameter controlling circuit which is controlled by data received from an external source with the data in the form of magnetic pulses of a width corresponding to the desired logic state of the parameter controlling signal. The transmitted signal contains both parameter data for controlling selected pacer parameter operation and access data which is processed by the implanted pacer for determining whether the parameter data is accepted for control purposes. To attempt to ensure proper receipt of the parameter data it is intermixed with access data and certain selected bits of the resulting binary word are compared within the implanted device after receipt with other selected bits of the binary word or with bits stored within the implanted device. However, all of the verification and comparison takes place within the implanted device.
The U.S. Pat. No. 4,142,533 to Brownlee et al., entitled "Monitoring System for Cardiac Pacers" discloses a system for telemetering and monitoring the functioning of an implanted pacemaker as well as controlling the testing of the functions from a remotely located facility. The implanted pacemaker contains a telemetry system comprising transmitting circuitry, including an FM monitoring oscillator, and associated control circuitry which is actuated to initiate selected tests. The transmitting functions as well as the monitoring functions are powered by the power supply of the implanted device. Historical operating data is not provided.
The U.S. Pat. No. 4,237,895 to Johnson, entitled "Control Signal Transmitter and Monitor for Implanted Pacer", discloses a system for encoding and transmitting commands to effect modifications in the operating characteristics of an implanted pacer. Means for detecting and displaying monitored pacer operation is also disclosed. An oscillator outputs a carrier signal which is modulated to exhibit a fixed number of signal pulses with the width of the pulses modulated to exhibit a first (longer) duration and a second (shorter) duration. A receiver in the external device detects signals outputted by the implanted device representing pacer operating characteristics. The implanted pacer has receiving means, detection means and data processing circuitry for receiving, assimilating and storing coded signals and a transmitting system responsive to received signals. The pacer transmits a modulated signal representing the operation of the pacer. A flip-flop and counter system detects the interval between the transmitted pulses.
The U.S. Pat. No. 4,026,305 to Brownlee et al., entitled "Low Current Telemetry System for Cardiac Pacers," discloses a system for telemetering the performance of an implanted cardiac pacer incorporating a low power, low voltage, frequency-voltage sensitive pulse generator which supplies a pulse-interval-modulated telemetry output. The telemetry system embodies a telemetry pulse generator which is sensitive to input voltage. The nominal carrier center frequency of the pulse generator is pulse-interval modulated by the voltage of the power cell of the implanted device. Further modulation of the carrier indicative of other parameters is accomplished by other voltage inputs.
The U.S. Pat. No. 4,232,679 to Schulman, entitled "Programmable Human Tissue Stimulator" discloses an externally programmable implanted tissue stimulator with provision within the implanted device for verifying and screening control parameter words which are transmitted from an external controller. Readout of the stimulating signals and the tissue response thereto is provided for. The implanted device includes a plurality of memories in which are stored different parameters including all parameters necessary to control the characteristics of the stimulating pulses provided by the implanted device. The implanted device includes receiving and decoding circuitry designed to receive digital signals in the form of multibit parameter words of unique formats and decode them. Special decoding criteria in the implanted device are employed to ensure that only parameter words not affected by noise are permitted to vary the contents of any parameter in the implanted device. Verification is accomplished by transmitting the contents of any one of the memories out of the implanted device to the external device.
The U.S. Pat. No. 4,223,679 to Schulman et al., entitled "Telemetry Means for Tissue Stimulator System," discloses a telemetry system for use in a living tissue stimulator system in which an externally located oscillator is controlled by impedance changes in an impedance reflecting circuit located in an implantable tissue stimulator. The impedance reflecting circuit is either an LC or LR circuit providing either frequency modulation or amplitude modulation of the signal generated by the external oscillator. The externally located oscillator drives an LC circuit in which the inductor is positioned in a magnetically coupled relationship to an inductor in the implanted impedance reflecting circuit. A signal to be telemetered modulates an output frequency of a voltage controlled oscillator located in the implanted device. This frequency modulated output of the voltage controlled oscillator drives an FET switch which alters the impedance of the impedance reflecting circuit thereby modulating the output of the externally located oscillator.
A series of prior art patents commonly owned by Medtronic, Inc. of Minneapolis, MN disclose a communications link to an implanted cardiac pacemaker. The communications method comprises a programming head with a permanent magnet therein to cause a magnetically actuated reed switch within the implanted device to close. The closure of the reed switch in the implanted device enables the implanted device to accept signals from the external device which consist of rf pulse bursts which are separated by either a long or short time period representing one or the other binary digit. The implanted device performs various functions upon the detected signal including a parity check, an access code check and determining if the proper number of signals were transmitted within a given time. The implanted device can then signal the acceptance of a programming signal or reset the program acceptance circuit if extraneous signals are detected as programming signals. This series of patents are U.S. Pat. No. 4,236,522 "Asynchronous/Demand Mode Programmable Digital Cardiac Pacemaker," No. 4,236,524 "Program Testing Apparatus", No. 4,241,736 "Reset Means for Programmable Digital Cardiac Pacemaker", No. 4,250,884 "Apparatus for and Method of Programming the Minimum Energy Threshold for Pacing Pulses to be Applied to a Patient's Heart", No. 4,250,883 "Digital Cardiac Pacemaker with Refractory, Reversion and Sense Reset Means" and No. 4,257,423 "Medical Device."
It is therefore a first object of the present invention to provide a two-way coherent inductive communications link between a biologically implanted programmable medical device and an external device.
It is a second object of the present invention to provide a two-way coherent inductive communications link between a biologically implanted programmable medical device and an external device that is reliable and accurate.
It is a third object of the present invention to provide a two-way coherent inductive communications link between a biologically implanted programmable medical device and an external device that is reliable and accurate with reprogramming data immediately verifiable.
It is a fourth object of the present invention to provide a two-way coherent inductive communications link between a biologically implanted programmable medical device and an external device wherein command and programming data can be transmitted to the biologically implanted programmable medical device.
It is a fifth object of the present invention to provide a two-way coherent inductive communications link between a biologically implanted programmable medical device and an external device wherein status and stored data can be transmitted to the external device.
It is a sixth object of the present invention to provide a two-way coherent inductive communications link between a biologically implanted programmable medical device and an external device wherein the transceiver in the implanted device is powered by the inductive field powered by the external device.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.